Allow files on a game page with no defined price to be marked as "Demo"

[Fonserbc]

Is your feature request related to a problem? Please describe.

I have a game page that is marked as "In Development" and does not have a defined price (No payments), but I want to be able to upload a demo and have itch acknowledge that the file I uploaded is a demo (using the demo feature tick for it)

Currently that is only possible if you mark the game as "Paid" and define a price (more than 1$), which itself is quite a hidden feature #324
But I don't want to show the price of my game anywhere yet. My game is still unreleased and in development, and the price is in discussion, and there seems to be no option to hide the price of a paid game.

Describe the solution you'd like

Allow "In development" games with a pricing defined as "No payments" to be able to mark a downloadable file as a demo, and make use of the feature, in order to inform players that the file is not just an early access file, but specifically is a demo.

Describe alternatives you've considered

The current alternative is to just mark the game as "No Payments" and just have the demo files available for download, but they do not display as "demo". You can change the display name to contain the word "Demo"